The Saemangeum Coast, located on the west side of the Korean peninsula, is undergoing a 30-year land reclamation project involving approximately 40 kilohectares. Because this project will drastically change the marine environment, monitoring and analyzing the water quality and marine life forms are necessary. However, the observation data are accumulating past the terabyte level, and the simulation data based on that data are also growing. Moreover, the gathered data are heterogeneous, and combining the datasets is often critical for gaining a better understanding of the environmental situation and for making predictions and decisions. A new visual-analytics tool for analyzing this situation fuses geographic-information-system data with ocean environmental data. It has three main components: data collection, geoprocessing, and data visualization. Researchers have used it to monitor and analyze changes in water quality, zooplankton distribution, and seabed topography.